Mars meteorite yields secret life

Above: modern magnetotactic bacteria showing chain of magnetite crystals. Below: chains of magnetite crystals in the Martian meteorite. Each chrystal is about one-millionth of an inch in diameter. Image - NASA AMES

Team leader Dr Imre Friedmann from NASA's Ames Research Center in California said such a chain of magnet-like objects could not have formed outside a living organism without it collapsing in on itself, due to magnetic forces.

"The end result looks somewhat like a string of pearls," Dr Friedmann said. Each magnetite crystal in the chain is a tiny magnet, approximately one-millionth of an inch in diameter.

The chains may have served as 'compasses' for the host magnetotactic bacteria, which may have used them to navigate.

The chains were preserved in the meteorite long after the bacteria themselves decayed and were captured using a scanning electron microscope.

The researchers say the magnetite chains were probably flushed into microscopic cracks inside the martian rock after it was shattered by an asteroid impact approximately 3.9 billion years ago. This cataclysmic event on Mars' surface may also have killed the bacteria. The same, or a later, asteroid impact ejected the rock, now a meteorite, into space.

Another NASA research group, led by Kathie Thomas-Keprta of NASA's Johnson Space Center, report in the same issue of PNAS that the magnetite crystals inside the meteorite are similar to those formed by 'modern' magnetotactic bacteria now living on Earth

Researchers say that if a small 1.8kg meteorite from Mars contained large numbers of bacteria, it is likely that such bacteria were widespread on the surface of Mars.

The presence of magnetotactic bacteria also suggests that oxygen-producing photosynthetic organisms were also present on Mars, because these bacteria need oxygen to survive.

The meteorite ALH84001 was found in the Allen Hills region of Antarctica in 1984 by researchers from the National Science Foundation, the Smithsonian Institute and NASA.

BBC News Online reports that the leader of a British project to land on Mars in 2003, Professor Colin Pillinger, described the study as very interesting, but says it falls short of absolute proof.

"We have to go to Mars and if there is doubt we will have to bring samples back. If there is still doubt we will have to send a person there to carry out the experiments in situ. Our Mars mission experiments are designed to test for organic matter and isotopic fractionation - the best measure I know to detect organic life," he added.

One major objection has been that the magnetite crystals could have come from bacteria which infiltrated the rock after it landed on Earth.

However, Dr Friedmann said the crystals were from Mars, because they are inside other globules of rock whose origin is uncontested.